Many multi-tenant office and residential buildings seek to provide heating and cooling which can be adjusted by the occupants of each conditioned space. In many instances this is provided by thermostat controlled central heating and air conditioning. However, in many applications, particularly in hotels or apartments, it is highly desirable to provide individual HVAC units for each conditioned space of the building. This is typically the case with hotels where individual preferences for temperature may vary greatly and efficient management of the hotel includes being able to greatly curtail heating or air conditioning to particular rooms or conditioned spaces when they are not being used.
Building code regulations typically require introduction of specified amounts of outside or ambient air into occupied interior spaces. While many standard room HVAC units are capable of introducing outside ambient air into a conditioned space, they are not capable of providing continuous dehumidification of the outside air supply to the conditioned space as conditions may require. Typically, dehumidification only occurs during room cooling when coolant is supplied to a cooling coil within the HVAC unit and the cooling coil is then at a temperature below the dew point of the outside or ambient air, thereby condensing excess humidity from the outside air. When the HVAC unit is not providing cooling to the conditioned space, outside air, which may be at high relative humidity, is directly introduced into the conditioned space. This leads to elevated levels of relative humidity within the conditioned space, which promotes microbial growth on interior surfaces within the space. As should be readily apparent, the less the space is cooled, the higher the relative humidity within the space rises and the more microbial growth is promoted. Thus, especially in hot, humid regions, cooling of outside air for dehumidification purposes is highly desirable. The alternative of continuously cooling all the air circulated through the HVAC unit can frequently cause over cooling of the conditioned space and is certainly not energy efficient as it requires cooling of the conditioned space during all times, even when the conditioned space is not in use.
Minimizing the consumption of energy while providing adequate ventilation and controlling the temperature and humidity within a conditioned space can lead to significant cost savings over the operational life of a building. Energy consumption can be minimized by only dehumidifying outside air when its ambient humidity requires dehumidification to control humidity within the conditioned space and by only introducing outside air within the conditioned space when it is occupied by a human.
One known solution to the above described problems is to provide a separate centralized ventilation system that includes dehumidification of outside air provided to each conditioned space. However, such a solution requires including air distribution duct work along with a centralized dehumidification system and controls, resulting in much greater initial construction costs. Moreover, it is cost prohibitive to retrofit existing buildings with such a separate, centralized, ventilation system. Furthermore, it circulates outside air to individual conditioned spaces whether or not they are occupied.
Another known solution to the problem of conditioning outside air to lower its humidity is an HVAC unit that continuously introduces outside or ambient air to the conditioned space with the ambient air being run over an outside air cooling coil circuit to dehumidify the outside air. A return air cooling coil circuit is provided for the cooling of return air from the conditioned space to provide cooling of the conditioned space on demand. Such a system, however, does not allow for introduction of outside air without cooling it whether or not dehumidification is necessary and further supplies outside air whether or not occupancy of the conditioned space dictates the need.
Yet another potential solution to the dehumidification of outside air, described in Rickert, U.S. Pat. No. 3,938,348, involves maintaining an evaporation coil at a select temperature below the dew point temperature of the outside air at all times the HVAC unit is in operation. When cooling is desired, return air from the conditioned space is run over the same coils concurrently with the outside air being dehumidified and the combined airflow is introduced to the conditioned space. However, this solution requires providing coolant to the entire coil during simple dehumidification and dehumidification in combination with cooling of the room, which is not energy efficient.
The present invention is directed toward overcoming one or more of the problems discussed above.